1. Field of the Invention
The present invention relates to an optical image reading apparatus, and more particularly to such an image reading apparatus capable of discriminating two or more colors of images from each other by irradiating reading spots on an original which bears the images.
2. Discussion of the Prior Art
An example of an optical image reading apparatus having a color discriminating function uses an optical reading head which has a plurality of yellow light-emitting elements LYn for producing yellow light beams, and a plurality of red light-emitting elements LRn for producing red light beams. The reading head has an image reading surface which extends along a platen on which an original bearing images to be read by the reading head is supported. The yellow light-emitting elements LYn are optically coupled to light-receiving ends of respective light-transmitting optical fibers Tn which are disposed such that their light-emitting ends are exposed on the image reading surface of the reading head. Similarly, the red light-emitting elements LRn are optically coupled to the light-receiving ends of the above-indicated light-transmitting optical fibers Tn which are disposed such that their light-emitting ends are exposed on the image reading surface. The light-emitting ends of the light-transmitting optical fibers are arranged in a straight row parallel to the platen, such that the light-emitting ends are equally spaced apart from each other.
The yellow light beams produced by the yellow light-emitting elements LYn and emitted from the light-transmitting optical fibers Tn toward the surface of the original are reflected by reading spots Sn on the surface, and the reflected yellow light beams are received by respective light-receiving optical fibers Rn whose light-receiving ends are located adjacent to the light-emitting ends of the respective light-transmitting optical fibers Tn. The yellow light beams received by the light-receiving optical fibers Rn are received by light-sensitive elements Pn. Similarly, the red light beams produced by the red light-emitting elements LRn and emitted from the light-transmitting optical fibers Tn are reflected by the reading spots Sn, and the reflected red light beams are also received by respective light-receiving optical fibers Rn and the light-sensitive elements Pn.
Initially, the line of reading spots Sn is irradiated with the yellow light beams. Output signals of the light-sensitive elements Pn are amplified by respective amplifiers An and applied to respective comparators Gn. Levels of the input signals of the comparators Gn are compared with predetermined reference or threshold values. Based on output signals of the comparators Gn, a suitable processing unit effects determination whether the reading spots Sn have a black or red color as distinguished from the base color (usually white) of the surface of the original. Namely, the irradiation of the reading spots Sn with the yellow light beams is effected to check each reading spot Sn for the presence of the black or red color. Then, the same line of reading spots Sn is irradiated with the red light beams, and output signals of the comparators Gn are obtained. Based on both the output signals of the comparators Gn upon irradiation of the reading spots Sn with the yellow light beams and the output signals of the same upon irradiation of the reading spots Sn with the red light beams, the processing unit determines whether the reading spot Sn which has been judged to have a black or red color as a result of the yellow beam irradiation is black or red.
Thus, each line of reading spots Sn is irradiated two times, one with the yellow light beams, and the other with the read light beams. In other words, the known optical image reading apparatus discussed above performs the second irradiation of the line of reading spots Sn with the red light, even if that line does not have any images (black and/or red dots). This leads to comparatively low image reading efficiency and economy.
As indicated above, the presence or absence of the black and red spots is determined based on the output signals of the comparators Gn when the reading spots Sn are irradiated with the yellow light beams. Further, the black and red spots are discriminated based on the output signals of the comparators Gn upon irradiation of the reading spots with the red light beams, in combination with the output signals upon the yellow beam irradiation. The original may have gray spots. In this case, the input level of the comparator Gn upon yellow beam irradiation of the gray spot may be either smaller or larger than the threshold value of the reference signal applied to the comparator Gn. When the input level of the comparator Gn upon the yellow beam irradiation is larger than the threshold value, the gray spot is judged to be white, irrespective of the input level of the comparator Gn upon the red beam irradiation of the gray spot. Since the gray spot is judged as a white spot, this does not practically cause a problem. However, if the input level of the comparator Gn upon the yellow beam irradiation is smaller than the reference value, the gray spot is judged to be either black or red, depending upon the input level of the comparator Gn upon the red beam irradiation. Where the input level is smaller than the reference value and the gray spot is judged to be black, the gray spot is printed as a black dot when the image data produced by the apparatus is used for printing. This may be tolerable since the printed document is just blurred by the black dot. However, the judgement of the gray spot as being red causes a problem, since the red dot in the non-imaged area of the printed document appears strange. Therefore, it is desirable to avoid the situation in which the input level of the comparator upon the red beam irradiation is larger than the threshold value when the input level of the comparator upon the yellow beam irradiation is smaller than the threshold value.
In the case where the original bears black images, the image reading by the reading head may be achieved by the yellow beam irradiation only. If corrections are inserted in red on the original, the red dots as well as the black dots are printed, when the image data produced by the apparatus is used for printing. Sometimes, however, it is desired that the original be printed without the red corrections. In this instance, it is required to reproduce the original without the red corrections, which requires extra time and cost.